The deal for 35% of Rock Creek gives the bank an option to take a majority stake in the firm. But it bought the stake through an asset management unit for boutique managers who are left to run their businesses more-or-less independently.

Financial terms of the arrangement were not disclosed. Wells Fargo said the deal will help it double its assets under management over the next seven years.

"We view this as one of the fastest-growing segments in the asset-management business," Mike Niedermeyer, head of Wells Fargo's asset management business, said. "While it's of a greater interest to larger clients, it's quickly becoming a larger area of focus for middle-size and smaller endowments, and state pension funds."

Niedermeyer said Wells Fargo may eventually move to make Rock Creek's products available to retail investors.

"We are so pleased to be partnering with one of the world's leading and most respected diversified financial services firms," Afsaneh Beschloss, the former World Bank chief investment officer who founder Rock Creek 10 years ago, said. "We believe this strategic partnership with Wells Fargo Asset Management will further enhance our ability to offer industry-leading solutions and services to our clients, while maintaining our corporate culture and institutional investment process."